Revertants of a streptomycin-resistant, spore-minus mutant of Bacillus subtillis were selected for the ability to sporulate. Spore-plus revertants were obtained which retain the streptomycin resistance mutations of the parent structure and have acquired additional mutations, some of which were shown to affect ribosomal proteins. Alterations in ribosomal proteins S4, S16 and L18 have been detected in these revertants by polyacrylamide gel electrophoresis. We plan to determine the location on the B. subtilis chromosomal map of the mutations causing the streptomycin-resistant, spore-minus phenotype of the parent strain, and the second-site mutations which suppress the asporogeny of the parent and cause the ribosomal protein alterations. Protein chemical studies on the mutant and wild type forms of the altered proteins will provide information about the nature of the mutations causing these alterations, i.e., whether they directly affect the structural genes for the ribosomal proteins or are involved in posttranslational modification. We will also examine the efficiency with which the spore-minus mutant and its revertants synthesize the sporulation-specific acid soluble spore proteins in vivo and in vitro